Field of the Invention
This invention relates to a semiconductor device that has a semiconductor chip connected in a flip chip manner.
Description of Related Art
To realize a size reduction and high-density packaging of a semiconductor device, attention has been paid to a flip chip connection structure in which a semiconductor chip is connected to a solid state device while causing a functional surface of the semiconductor chip on which a functional element 54 is formed to face the solid state device.
FIG. 4 is a diagrammatic sectional view of a semiconductor device having a flip chip connection structure. This semiconductor device 51 includes a wiring board 52 and a semiconductor chip 53 connected to a surface 52a of the wiring board 52 while causing a functional surface 53a of the semiconductor chip 53 to face the surface 52a of the wiring board 52.
A rectangular connection pad 58 is formed on the surface 52a of the wiring board 52. The wiring board 52 and the semiconductor chip 53 are bonded and electrically connected together with a predetermined interval therebetween by means of a connecting member 55 connected to the connection pad 58. A solder resist film 56 that has a thickness smaller than an interval between the surface 52a of the wiring board 52 and the functional surface 53a of the semiconductor chip 53 is formed on the surface 52a. 
The solder resist film 56 has a rectangular opening 56a by which the connection pad 58 is exposed. As shown in FIG. 5, the opening 56a is greater in size than the connection pad 58 when viewed in plane. The connecting member 55 is connected to the connection pad 58 in the opening 56a. 
A slight gap is formed between the surface of the solder resist film 56 and the functional surface 53a of the semiconductor chip 53. This gap is sealed with an underfill layer 57. The underfill layer 57 is formed such that the wiring board 52 and the semiconductor chip 53 are bonded together, and then a liquid underfill material is injected therebetween.
In more detail, after the wiring board 52 and the semiconductor chip 53 are bonded together, a dispenser 60 is disposed near the outer peripheral part of the semiconductor chip 53 as shown in FIG. 6A, whereafter a liquid underfill material 57P is poured between the surface of the solder resist film 56 and the functional surface 53a of the semiconductor chip 53 from the dispenser 60. Capillarity causes the underfill material 57P to enter and spread between the surface of the solder resist film 56 and the functional surface 53a of the semiconductor chip 53 as shown in FIG. 6B. When the whole area between the surface of the solder resist film 56 and the functional surface 53a of the semiconductor chip 53 is filled with the underfill material 57P, the dispenser 60 stops discharging the underfill material 57P. Thereafter, the underfill material 57P is hardened, whereby the underfill layer 57 is obtained (see Chee Choong Kooi and six others, “Capillary Underfill and Mold Encapsulation Materials for Exposed Die Flip Chip Molded Matrix Array Package with Thin Substrate”, 2003 Electronics Packaging Technology Conference, pp. 324-330).
However, a level difference locates between the inside and the outside of the opening 56a, and a space over the opening 56a is restricted by the semiconductor chip 53. Therefore, disadvantageously, when the underfill material flows into the opening 56a, air that exists around the periphery of the opening 56a (i.e., exists in a portion having the level difference) is taken into the underfill material without sufficiently going out therefrom, and, as a result, a so-called void 61 is generated in the underfill layer 57. For example, if a void is generated in the underfill layer 57, a crack will appear in the underfill layer 57 at a reflow step, thus causing a decrease in reliability of the semiconductor device.